It's Parliament that decides who we can and can't marry. It's not decided by a committee of clergy. Or handed down by Holy Writ.

The regulation of marriage in New Zealand began with an ordinance in 1842 and the first Marriage Act was passed on the establishment of Parliament in 1854.

Our present Marriage Act dates from 1955. It sets out the rules for who can and can't marry. For example, the act prohibits a man marrying his former wife's grandmother or his daughter's son's wife. It's fortunate that Parliament thought of such possibilities and prohibited them.

The Marriage Act 1955 doesn't say I can't marry a man or that a woman can't marry a woman.

But the courts have ruled that it wasn't Parliament's intent to enable same-sex marriage and that it's up to Parliament, not the courts, to declare whether same-sex marriages are lawful, not the courts. It's a fair call.

Back when the Marriage Act was enacted, homosexual activity was a crime carrying a maximum of life imprisonment. It's a safe bet that parliamentarians then weren't envisaging they were passing a law that would enable two men to apply for a marriage licence.

But even then the law had softened towards homosexuality.

Parliamentarians in the early days were hard core and set the penalty for homosexual activity as death. The death penalty for buggery was removed in 1867.

The 1893 New Zealand Criminal Code was still discouraging: "Everyone is liable to imprisonment with hard labour for life, and, according to his age, to be flogged or whipped, once, twice or thrice, who commits buggery either with a human being or with any other living creature".

The flogging for buggery was removed in 1941 and hard labour removed in 1954.

The big change was in 1986, when Parliament voted by a narrow margin to decriminalise homosexual activity. Consensual sex between men was no longer a crime.

Consensual sex between women was never illegal in New Zealand. Early legislators thought such a thing impossible and didn't like to think about it and so never criminalised it.

Once homosexual acts were decriminalised in 1986 the inability of homosexuals to marry was an obvious anomaly and inequality. Homosexuals can have consensual sex; they just can't get married to do so.

In 2005 Parliament fudged the issue by allowing civil unions.

A civil union is everything a marriage is - it just has a different name. The crucial difference is that same-sex couples can have a civil union.

The thinking at the time was that civil unions legislation might succeed in Parliament but allowing homosexuals to marry would not.

The civil union law passed by 65 votes to 55.

Since then, 2000 New Zealand couples have tied the knot through civil union. One in five were heterosexual couples; nearly half were female plus female; a third were male plus male; 83 civil unions have been dissolved.

Importantly, the sky has not fallen. Certainly civil unions haven't proved "destructive of the very foundations of society as we know it" as the critics feared. And now MP Louisa Wall's Marriage (Definition of Marriage) Amendment Bill has been drawn from the ballot.

The way the ballot works is that Parliament sets aside limited time to consider legislation put up by MPs. Ordinarily it's only government ministers who can introduce legislation. Which members' bills get considered is determined by ballot.

That's how Louisa Wall's bill has arrived before Parliament. It was her call, and the luck of the draw.

Her bill is a simple one: it amends the Marriage Act to declare that "marriage means the union of two people, regardless of their sex, sexual orientation, or gender identity".

The bill will be subject to a "conscience" or free vote. Each MP has a vote and it is up to each of them individually how they vote.

That makes the final vote hard to predict and there will be intense lobbying of individual MPs.

I have enormous respect for conservative values and traditional ways of doing things. But here's the question for those pushing traditional values against same-sex marriage: what tradition do you want our Parliament to push back to? The death penalty? Flogging? Hard labour? Life imprisonment? Seven years' jail?

Our Parliament has a sad and sorry history in its treatment of two adults who just want to love and be with one another.

Let's hope with Louisa Wall's bill that history is finally made just that: history.